Baby's particles

Not even a fragment... None of the baby remained on me. I knew it to be true but still couldn't help looking at my palm for a sign. Never again would I encounter the baby. Never. The finality of it struck me once again.

„

—Samus Aran

Samus catches a particle in her palm.

The baby's particles were remnants from the baby's death as depicted in Metroid: Other M. After it explodes above Samus, it becomes a rain of particles that fall over her like snow.

The particles serve as a hypothetical explanation for how Samus gains the Hyper Beam, as she catches one in her hand. It is possible that energy from the Laser Brain Attack was stored in the particle and it filled her Arm Cannon with the energy, and this, combined with her empowerment over the baby's death, created the Hyper Beam.

No particles were seen in the original version of Super Metroid, likely due to sprite limitations; instead, the baby fell toward an exhausted Samus while constantly exploding, until she began to flash and stand up, ready to defeat Mother Brain.